Coordination Chemistry of Organoruthenium Compounds with Benzoylthiourea Ligands and their Biological Properties

Molecular insight into the structural and functional aspects of arene Ru(II) complexes bearing bulky thiourea ligands

Herein we report four new arene ruthenium(II) complexes [RuII(η6-p-cymene)(L1)к1(S)Cl2] (C1), [RuII(η6-benzene)(L1)к1(S)Cl2] (C2) where L1 is N-((2,6-dimethylphenyl)carbamothioyl)benzamide (L1), and [RuII(η6-p-cymene)(L2)к1(S)Cl2] (C3), [RuII(η6-benzene)(L2)к1(S)Cl2] (C4) where L2 is N-((2,6-diisopropylphenyl)carbamothioyl)benzamide (L2) which were synthesized and evaluated for biological activity. The monodentate coordination of thione sulphur (S) to ruthenium ion along with two terminal chloride was confirmed by X-Ray diffraction analysis thus revealing a typical "piano-stool" pseudo tetrahedral geometry. DPPH radical scavenging activity showed that ligands were less efficient however on complex formation it showed significant efficacy with C4 showing the highest activity. The ligands and ruthenium complexes exhibited minimal to no cytotoxic effects on HEK cells within the concentration range of 10-300 μM. Evaluating the cytotoxicity against prostate cancer cells (DU145) L1, L2 and C1 displayed more pronounced cytotoxic activity with C1 showing high cytotoxicity against the cancer cells, in comparison to cisplatin indicating its potential for further investigation and analysis. Considering this, compound C1 was used to further study its interaction with BSA using fluorescence spectroscopy and it was found to be 2.64 × 106 M-1. Findings from CD spectroscopy indicate the binding in the helix region which was further confirmed with the molecular docking studies.

Exploration of newly synthesized amantadine-thiourea conjugates for their DNA binding, anti-elastase, and anti-glioma potentials

Three newly synthesized amantadine thiourea conjugates namely MS-1 N-(((3 s,5 s,7 s)-adamantan-1-yl)carbamothioyl)benzamide, MS-2 N-(((3 s,5 s,7 s)-adamantan-1-yl)carbamothioyl)-4-methylbenzamide and MS-3 N-((3 s,5 s,7 s)-adamantan-1-ylcarbamothioyl)-4-chlorobenzamide were investigated for their structures, bindings (DNA/ elastase), and for their impact on healthy and cancerous cells. Theoretical (DFT/docking) and experimental {UV-visible (UV-), fluorescence (Flu-), and cyclic voltammetry (CV)} studies indicated binding interactions of each conjugate with DNA and elastase enzyme. Theoretically and experimentally calculated binding parameters for conjugate - DNA interaction revealed MS-3 - DNA to have most significant binding with comparatively greater values of binding parameters {(Kb/M-1: docking, 3.8 × 105; UV-, 5.95 × 103; Flu-,1.55 × 105; CV, 1.52 × 104), (∆G/ kJmol-1: docking, -32.09; UV-, -22.40; Flu-,-30.81; CV, -24.82)}. The docked structures, greater bindings site size values (n), and the trend in DNA viscosity changes in the presence of each conjugate concentration confirmed a mixed binding mode of interaction among them. Conjugate - elastase binding by docking agreed with the experimental anti-elastase findings. Cytotoxicity studies of each tested conjugate demonstrated greater cytotoxicity for cancerous (MG-U87) cells in comparison to control, while for the normal (HEK-293) cells the cytotoxicity was found comparatively low. Overall exploration suggested that MS-3 is the most effective candidate for DNA binding, anti-elastase, and for anti-glioma activities.

Anticancer Properties of Ru and Os Half-Sandwich Complexes of N,S Bidentate Schiff Base Ligands Derived from Phenylthiocarbamide

The versatile coordinating nature of N,S bidentate ligands is of great importance in medicinal chemistry imparting stability and enhancing biological properties of the metal complexes. Phenylthiocarbamide-based N,S donor Schiff bases converted into RuII /OsII (cymene) complexes and characterized by spectroscopic techniques and elemental analysis. The hydrolytic stability of metal complexes to undergo metal-halide ligand exchange reaction was confirmed both by the DFT and NMR experimentation. The ONIOM (QM/MM) study confirmed the histone protein targeting nature of aqua/hydroxido complex 2 aH with an excellent binding energy of -103.19 kcal/mol. The antiproliferative activity against a panel of cancer cells A549, MCF-7, PC-3, and HepG2 revealed that ruthenium complexes 1 a-3 a were more cytotoxic than osmium complexes and their respective ligands 1-3 as well. Among these ruthenium cymene complex bearing sulfonamide moiety 2 a proved a strong cytotoxic agent and showed excellent correlation of cellular accumulation, lipophilicity, and drug-likeness to the anticancer activity. Moreover, the favorable physiochemical properties such as bioavailability and gastrointestinal absorption of ligand 2 also supported the development of Ru complex 2 a as an orally active anticancer metallodrug.

Ru(II)-p-Cymene Complexes of Furoylthiourea Ligands for Anticancer Applications against Breast Cancer Cells

Half-sandwich Ru(II) complexes containing nitro-substituted furoylthiourea ligands, bearing the general formula [(η⁶-p-cymene)RuCl₂(L)] (1-6) and [(η⁶-p-cymene)RuCl(L)(PPh₃)]⁺ (7--12), have been synthesized and characterized. In contrast to the spectroscopic data which revealed monodentate coordination of the ligands to the Ru(II) ion via a "S" atom, single crystal X-ray structures revealed an unusual bidentate N, S coordination with the metal center forming a four-membered ring. Interaction studies by absorption, emission, and viscosity measurements revealed intercalation of the Ru(II) complexes with calf thymus (CT) DNA. The complexes showed good interactions with bovine serum albumin (BSA) as well. Further, their cytotoxicity was explored exclusively against breast cancer cells, namely, MCF-7, T47-D, and MDA-MB-231, wherein all of the complexes were found to display more pronounced activity than their ligand counterparts. Complexes 7-12 bearing triphenylphosphine displayed significant cytotoxicity, among which complex 12 showed IC₅₀ values of 0.6 ± 0.9, 0.1 ± 0.8, and 0.1 ± 0.2 μM against MCF-7, T47-D, and MDA-MB-231 cell lines, respectively. The most active complexes were tested for their mode of cell death through staining assays, which confirmed apoptosis. The upregulation of apoptotic inducing and downregulation of apoptotic suppressing proteins as inferred from the western blot analysis also corroborated the apoptotic mode of cell death. The active complexes effectively generated reactive oxygen species (ROS) in MDA-MB-231 cells as analyzed from the 2',7'-dichlorofluorescein diacetate (DCFH-DA) staining. Finally, in vivo studies of the highly active complexes (6 and 12) were performed on the mice model. Histological analyses revealed that treatment with these complexes at high doses of up to 8 mg/kg did not induce any visible damage to the tested organs.

Platinum(terpyridine) complexes with N-heterocyclic carbene co-ligands: high antiproliferative activity and low toxicity in vivo

Pt(terpyridine) complexes are well-known DNA intercalators. The introduction of an NHC co-ligand rendered such a complex highly antiproliferative in cancer cells compared to its chlorido derivative. Despite the high potency, zebrafish embryos tolerated the compound well, especially compared to cisplatin. DNA interaction studies support a mode of action related to intercalation.

Impact of Coordination Mode and Ferrocene Functionalization on the Anticancer Activity of N-Heterocyclic Carbene Half-Sandwich Complexes

The substitution of phenyl rings in established drugs with ferrocenyl moieties has been reported to yield compounds with improved biological activity and alternative modes of action, often involving the formation of reactive oxygen species (ROS). Translating this concept to N-heterocyclic carbene (NHC) complexes, we report here organometallics with a piano-stool structure that feature di- or tridentate ligand systems. The ligands impacted the cytotoxic activity of the NHC complexes, but the coordination modes seemed to have a limited influence, which may be related to the propensity of forming the same species in solution. In general, the stability of the complexes in an aqueous environment and their reactivity to selected biomolecules were largely dominated by the nature of the metal center. While the complexes promoted the formation of ROS, the levels did not correlate with their cytotoxic activity. However, the introduction of ferrocenyl moieties had a significant impact on the antiproliferative potency of the complexes and, in particular, some of the ferrocenyl-functionalized compounds yielded IC₅₀ values in the low μM range.

Novel adamantyl clubbed iminothiazolidinones as promising elastase inhibitors: design, synthesis, molecular docking, ADMET and DFT studies

Porcine Pancreatic Elastase (PPE) is a serine protease that is homologous to trypsin and chymotrypsin that are involved in various pathologies like inflammatory disease, Chronic Obstructive Pulmonary Disease (COPD), acute respiratory distress syndrome, cystic fibrosis, and atherosclerosis. PPE if remained uninhibited would lead to digestion of important connective tissue. We developed new structurally diverse series of adamantyl-iminothiazolidinone hybrids to divulge elastase inhibition assay. To identify potent derivatives, in silico screening was conducted and in vitro studies disclosed that the compounds 5a, 5f, 5g, and 5h showed excellent binding energies and low IC₅₀ values. In silico studies including molecular docking, DFT studies (using the B3LYP/SVP basis set in the gas phase) drug likeness scores and molecular dynamic simulation studies were conducted to evaluate protein–ligand interactions and to determine the stability of top ranked conformation. In silico studies further supported the results of in vitro experiments and suggest these derivatives as novel inhibitors of elastase enzyme.

Structurally diverse adamantyl-iminothiazolidinone conjugates were synthesized, evaluated for elastase inhibition, and subjected to in silico ADMET prediction. The inhibition studies revealed compounds 5a, 5f, 5g, and 5h to show significant activity.

Impact of aliphatic acyl and aromatic thioamide substituents on the anticancer activity of Ru(II)-p-cymene complexes with acylthiourea ligands-in vitro and in vivo studies

Six different acylthiourea ligands (L1-L6) and their corresponding Ru(II)-p-cymene complexes (P1-P6) were designed to explore the structure-activity relationship of the complexes upon aliphatic chain and aromatic conjugation on the C- and N-terminals, respectively. The compounds were synthesized and adequately characterized using various analytical and spectroscopic techniques. The structures of P2-P6, solved using single crystal X-ray diffraction (XRD), confirmed the neutral monodentate coordination of the S atoms of the acylthiourea ligands to Ru(II) ions. In silico studies showed an increase of lipophilicity for the ligands with an increase in alkyl chain length or aromatic conjugation at the C- or N-terminal, respectively. Subsequently, mitogen-activated protein kinases (MAPK) were predicted as one of the primary targets for the complexes, which showed good binding affinity towards extracellular signal-regulated kinases (ERK1, ERK2 and ERK5), c-Jun N-terminal kinase (JNK) and p38 of the MAPK pathway. Henceforth, the complexes were tested for their anticancer activity in lung carcinoma (A549) and cisplatin-resistant lung carcinoma (cisA549R) cells and human umbilical vein epithelial normal cells (HUVEC). Interestingly, an increase in chain length or aromatic conjugation led to an increase in the activity of the complexes, with P5 (7.73 and 13.04 μM) and P6 (6.52 and 14.45 μM) showing the highest activity in A549 and cisA549R cells, which is better than the positive control, cisplatin (8.72 and 44.28 μM). Remarkably, we report the highest activity yet observed for complexes of the type [(η6-p-cymene)RuIICl2(S-acylthiourea)] in the tested cell lines. Aqueous solution studies showed that complexes P5 and P6 are rapidly hydrolyzed to produce solely aquated species that remained stable for 24 h. Staining assays and flow cytometric analyses of P5 and P6 in A549 cells revealed that the complexes induced apoptosis and arrested the cell cycle predominantly in the S phase. In vivo studies demonstrated the higher toxicity of cisplatin and a comparatively higher survival rate of mice injected with the most active complex P6. Histological analyses revealed that treatment with P6 at high doses of up to 8 mg kg-1 did not cause any palpable damage to the tested organs.

Mustards-Derived Terpyridine-Platinum Complexes as Anticancer Agents: DNA Alkylation vs Coordination

The development of bifunctional platinum complexes with the ability to interact with DNA via different binding modes is of interest in anticancer metallodrug research. Therefore, we report platinum(II) terpyridine complexes to target DNA by coordination and/or through a tethered alkylating moiety. The platinum complexes were evaluated for their in vitro antiproliferative properties against the human cancer cell lines HCT116 (colorectal), SW480 (colon), NCI-H460 (non-small cell lung), and SiHa (cervix) and generally exhibited potent antiproliferative activity although lower than their respective terpyridine ligands. ¹H NMR spectroscopy and/or ESI-MS studies on the aqueous stability and reactivity with various small biomolecules, acting as protein and DNA model compounds, were used to establish potential modes of action for these complexes. These investigations indicated rapid binding of complex PtL3 to the biomolecules through coordination to the Pt center, while PtL4 in addition alkylated 9-ethylguanine. PtL3 was investigated for its reactivity to the model protein hen egg white lysozyme (HEWL) by protein crystallography which allowed identification of the N^δ1 atom of His15 as the binding site.

1,1′,3,3′-Tetramesitylquinobis(imidazole)-2,2′-dithione

The solid-state structural analysis of the title compound [systematic name: 5,11-disulfanylidene-4,6,10,12-tetrakis(2,4,6-trimethylphenyl)-4,6,10,12-tetraazatricyclo[7.3.0.03,7]dodeca-1(9),3(7)-diene-2,8-dione], C44H44N4O2S2 [+solvent], reveals that the molecule crystallizes in a highly symmetric cubic space group so that one quarter of the molecule is crystallographically unique, the molecule lying on special positions (two mirror planes, two twofold axes and a center of inversion). The crystal structure exhibits large cavities of 193 Å3 accounting for 7.3% of the total unit-cell volume. These cavities contain residual density peaks but it was not possible to unambiguously identify the solvent therein. The contribution of the disordered solvent molecules to the scattering was removed using a solvent mask and is not included in the reported molecular weight. No classical hydrogen bonds are observed between the main molecules.

Anticancer organorhodium and -iridium complexes with low toxicity in vivo but high potency in vitro: DNA damage, reactive oxygen species formation, and haemolytic activity

Dinuclear Rh^III(Cp*) and Ir^III(Cp*) complexes demonstrated potent in vitro anticancer activity while exhibiting low toxicity in haemolysis studies and in vivo zebrafish models.